Std Enthalpy of Formn: The Fourth Way!
VAHS
M
This is material for Test 5 – May 16
I.
The average bond energies method. (this is the least accurate but it is easy to do if you know the molecule's structure) bottom of the green sheet
II.
The Hess's Law method. (this is very accurate but it may be hard to look up the appropriate stacked reactions to add together).
III.
The standard enthalpies method (very accurate, thousands of substances have easy to look up data) top of the green sheet
IV.
The calorimeter method: go and actually do the reaction yourself in a calorimeter so you can measure the heat.
(accurate if you have expensive equipment and are skillful )
1) Lithium hydroxide is a white, basic solid. a.
write the formula of lithium hydroxide _______ b.
write the balanced reaction and energy for formation of one mole of solid lithium hydroxide from its elements in their standard states:
ΔH = ( ) ___________ + ___________ + ___________ --> ___________
2) The melting ice in Greenland is easy to measure precisely by satellite. How does the GRACE satellite measure the amount of ice in Greenland?

3)
Use standard enthalpies of formation to calculate the change of enthalpy at standard conditions for the following reactions. The reaction may need to be balanced first. For this assignment, so that we all use the same balancing numbers, let’s arbitrarily agree to make the coefficients the smallest whole numbers possible. a.
H
2
SO
4(aq)
+ 2CsCl
(cr)
 CsSO
4(cr)
+ HCl
(aq) b.
SO
3(g)
+ H
2
O
(g)
 H
2
SO
4(aq)
4) Many colas contain phosphoric acid, H
3
PO
4
. . a.
write the formula of phosphoric acid _______ b.
write the balanced reaction and energy for formation of one mole of aqueous phosphoric acid from its elements in their standard states:
ΔH = ( ) ___________ + ___________ + ___________ --> ___________
5) The four methods we have tried all have differing accuracy. For example, the reaction of
½N
2(g)
+ 3/2H
2(g)
--> NH
3(g)
: a.
What is the Lewis dot structure of each of these substances? b.
According to the AVERAGE BOND ENERGIES method, what is the enthalpy of this reaction? c.
According to the STANDARD ENTHALPY method, what is the enthalpy of this reaction? d.
Use the formula for percent error to estimate the error associated with using the method of average bond energies. It is safe to consider the result from part C above as the
.

6) In chemistry, the letter "H" stands for
. What do all of these other symbols stand for? a) ____________________________________________ b) ____________________________________________ c) ____________________________________________
7) Ocean buoy measurements have shown that the top layer of the world's oceans is growing warmer and is continuing to grow warmer. This is evidence that a.
the energy entering earth from the sun is less than the energy leaving earth to space b.
the energy entering earth from the sun is equal to the energy leaving earth to space c.
the energy entering earth from the sun is greater than the energy leaving earth to space
8) Polar ice area can decrease for a variety of reasons but once the ice melting begins, a feedback effect can occur. When Earth's ice-covered area decreases, what three feedback loops that cause even further ice to melt? a.
. b.
. c.
.
9) Use standard enthalpies of formation to calculate the change of enthalpy at standard conditions for the following reaction. Make the coefficients the smallest whole numbers possible.
TiO
2(cr)
+ H
2(g)
--> Ti
(cr)
+ H
2
O
(L)
10) Not many people would let you burn their diamonds but with method 3 you don't need to to measure the heat it would give off. The ΔH f
°for
C(diamond) is shown here  a.
Write the reaction for combustion of a diamond, with the only product being one mole of carbon dioxide gas.
________ + ________ --> __________ b.
Calculate the enthalpy change for the reaction you wrote in part (a) just now. c.
In the comic Superman
©
, The Man of Steel could famously change a piece of coal into a diamond by squeezing it in his hands. Assuming that coal is mostly graphite, write a reaction equation for changing coal into a diamond. Don't work too hard; the reaction has only one reactant and one product, both shown in the table above.
__________ --> ___________ d.
Based on only ΔH calculations, would Superman's hands feel warm or cold? Show your math as proof.